Method of applying protective coatings to sheets



Patented Sept. 16, 1941 METHOD OF APPLYING PROTECTIVE COAT- INGS TOSHEETS Henry L. Kohler, Kansas City, Mo., assignor to Andrew A. Kramer,Kansas City, M0.

N Drawing. Application october 8, 1938, Serial No. 234,049

1 Claim. (01. 91-681) My invention relates to a method of applyinprotective coatings to sheets, and more particularly to a method ofapplying a protective coating to a galvanized steel sheet. Thisapplication is a continuation in part of my co-pending applicationSerial No. 144,029, filed May 21, 1937,

patented March 21, 1939, Patent No. 2,150,929.

It is an important purpose of my invention to provide means forovercoming the difliculty that has previously existed in the utilizationof galvanized metallic sheets having a heavy coating of galvanizing,which was, that when the sheets were bent, the coating of zinc at thebend would tend to crack and peel, or flake off. As pointed out in theabove mentioned patent, the bending of a sheet to form a flange, orseam, would, due to this tendency of the zinc, damage the galvanizingcoating so seriously that it would render the coating at least partiallyineffective where the bends required to form such flanges, or seams,were made, and as a result the advantage of the heavy galvanized coatingon the sheet was largely lost. This, as has been pointed out in saidabove mentioned application, is true because a sheet, the galvanizedcoating of which had been ruptured by the bending operation, would be nobetter than an uncoated sheet, as far as resistance to oxidation, orother corrosion, was concerned, at the rupture, although the remainderof the sheet would be still well coated. While other more expensive anddiflicult-to-perform methods have been attempted for overcoming thisdiiiiculty, my invention has for its purpose the provision of means forprotecting a sheet that has'been fabricated, in a manner so as toprevent any corrosion thereof at a bend, or bends,,even though theoriginal zinc coating may have been ruptured or damaged in making thebend. h

It is a further important purpose ofmy invention to provide a protectivecoating at the bend, or bends, in a galvanized metallic sheet, that willbe even more resistant to corrosion, due to certain causes, than thegalvanized sheet was before bending or fabrication thereof, and whichwill resist every kind of corrosion equally as well, as does thegalvanized sheet at the portions thereof that have only the heavygalvanizing coating thereon applied prior to its fabrication. Byfabrication of the sheet is meant any bending, cutting or punchingoperation, or other such operation, that may be performed on the sheetafter the same has been rolled and galvanized.

My improved method of providing a protective coating on the sheet can beutilized, for not only protecting, or making the sheet more resistant tocorrosion, at a bend therein where the galvanizing coating may have beendamaged, or-

ruptured, but may be utilized to give a better protective coatingagainst certain'types of corrosion, or due to certain causes, over theentire area of the sheet, if this is desired, the treatment of the sheetto obtain this greater protection against corrosion being given to thesheet after it has been rolled and galvanized and labricated, as definedabove. Thus in a tank that is filled with a liquid that may have anundesirable corrosive effect on the usual zinc coating used on agalvanized sheet, the entire inner surface of the tank sections orsheets, fabricated to a shape and size and punched with suitable holesfor securing the sections together, may be treated to make the same moreresistant to corrosion, as well as the bends therein, if there be any inthe section. Of course, if it is only desired to cure a defect in thecoating at a bend in a sheet, it is only necessary to treat the zinccoated sheet on the sides of the bends which are outermost, that is, onthe outside of the bends.

This is true because the zinc coating is not injured on the inner sideof the bend, 'as it is due to its lack of tensile strength thattherupturing, or damaging, of the zinc coating occurs.

As has been pointed out in the above mentioned patent, the zinc coatingon a galvanized iron or steel sheet, comprises an inner'coating, that isa ferrous zinc alloy, adjacent the iron and a pure zinc layer overlyingthe ferrous zinc alloy, the thickness and depth of this pure zinccoating, or layer, depending upon the number of times that the sheet isrun through the galvanizing bath, or other details of the process ofgalvanizing, which are not of importance here. The heavier the coatingof zinc obtained on the sheet the greater the difliculty in preventingcracking of the galvanizing or zinc coating, due to making a sharp bendin the sheet or performing other operations on the sheet that mightrupture or crack the same, this being due to the fact that the tensilestrength of the zinc is very much less than that of either the steel orthe ferrous zinc alloy. My invention entirely overcomes the difficultyresulting from the rupthis occurs, the

sistant to corrosion due to-sulphur compounds present in certain oilsand similar materials, that may be confined in tanks that aremanufactured out of galvanized sheets, such as above referred to.

This is accomplished by amalgamating mercury with the protective coatingat the bend in the sheet at which the rupture/of the galvanizing coatingmay have occurred, or with the coating over the surface of the sheetthat is desired to be protected against corrosion, such as a sheet usedin a tank, the inner surface of which is to be particularly wellprotected against corrosion. Mercury and amalgams of mercury areparticularly resistant to corrosion and are not affected by hydrogensulphide as is zinc, the same being particularly resistant to corrosiondue to acids, such as sulphuric acid, and other acids, and compounds,that may be encountered in the use of'fabricated galvanized steel or"iron sheets. While metallic mercury function of the temperature andthickness of the zinc coating. The method further comprises a methodofapplying mercury to a galvanized metallic sheet to amalgamate with thezinc coating thereon, by spreading a soft putty-like amalgam of mercuryand. tin, or similar metal, on the area of the sheet over which themercury is tolbe amalgamated with the zinc.

Other objects and advantages of my invention will appear as thedescription of the same proceeds.

ever,- that I do not intend to limit myself to can be used to produce anamalgam coating on a I and a metal that freely dissolves in mercury,-

or readily amalgamates therewith, to the surface to be protected. I havefound that an amalgam of the consistency of soft putty, of a creamycharacter; if rubbed on the metal at the place where it is to beprotected, such as a rupture in the coating on the sheet, causes acertain amount of the amalgam to adhere to the surface of the sheet,both at the zinc coated area and the area where the coating has beenruptured. Due to the character and consistency of theamalgam, the excesscan be readily removed with a cloth, or'in a similar manner, and savedfor future use. Preferably, a. tin-mercury amalgam is utilized for thispurpose, producing a tin-zinc-mercury amalgam coating. f

Specifically it is a purpose of my invention to provide a method offorming a corrosion re-' sisting coating on a galvanized metallic sheet,comprising making a putty-like amalgam of mercury and tin, spreadingsaid tin-mercury amalgam over the zinc coating on said sheet whereverdesired, whether at ruptures therein or otherwise, and leaving theamalgam, adhering to the sheet, undisturbed thereon long enough that itwill be amalgamated with the zinc on the sheet, to form thetin-zinc-mercury amalgam coating referred to above. when this occurs itcan be readily recognized, as the. coating willat first be soft and canbe rubbed off with the fingers, but after twenty-four to fortyeighthours, the coating will be just as hard and have a similar appearance tothat on the sheet before the amalgam was applied thereto. when 'tratedthe zinc coating at least down to the ferrous zinc alloy at the surfaceof the steel or iron, and formed, with the zinc on the sheet,

a zinc-tin-mercury amalgam. The action above rapidly in warmweathroceeds more dmflbed p at which penetration er than in cold, therate tin-mercury amalgam has penethe particulardetails described, exceptas defined in the claim. I a

My improved method is carried out on galvanized sheets that have beenfabricated to the desired size and shape, by bending, die-shaping,cutting and punching operations, or any of these that may be necessaryto produce the article, or sections of an article, of the desired shapefrom the sheet of metal.- After the sheet has been fabricated, it iscleaned at the places at which the protective coating is-to be providedthereon, usually by means of dilute hydrochloric acid, or a solution oftin chloride, or antimony chloride, or lead chloride, or zinc chloride,or cyanide of soda to remove zinc oxide, oil and dirt from thegalvanized sheet.- This cleaning solution may be applied with a brush orswab of some character, and the excess may be removed with a cloth, orany other suitable means. When it is desired to apply the protectivecoating only at or adjacent a ruptured area on a galvanized sheet, or anarea that may have been damaged to the extent of injuring the protectivecoating, or rupturing the same, the galvanized sheets are cleaned onlyon the outer sides of all bends therein, or any other area at which thecoating may have been ruptured, or damaged, and areas adjacent thesebends, or other areas where the damage may have occurred. A zone at theplace at which the rup-.

ture in the zinc coating may exist will thus be cleaned, and also a zoneon each side thereof.

A putty-like amalgam of mercury and a metal readily dissolving therein,or amalgamatin therewith, such as tin, is made up prior to cleaning thesheets, or is made up in quantity, to be used whenever necessary, saidamalgam having such proportions of the metal, such as tin, and mercurytherein, asto produce'a soft putty-like material of a consistency 'ofthick paste, or cream. The proportions of mercury and the other metalamalgamating therewith that are used to produce this soft putty-likecoating material, will vary with the-metals used and with theatmospheric temperature existing, as the material must, of course, beofthe soft, creamy putty-like character at the temperature at which it isapplied to the sheet. Thus in the winter time, when a lower temperatureis encountered,

both in the atmosphere and in the sheets themselves, a larger proportionof mercury to the tin,

of .the zinc by the amalgam occurs being a of tin by weight will producean amalgam of the desired consistency in the summer time, while in thewinter time when the. temperatures are exceedingly low, it is frequentlynecessary to utilize an amalgam madefor this purpose, that is made up ofone part by weight of tin to two parts by temperatures are encountered,even one part by weight of tin to three parts by weight of met-- Idesire to have it understood, howeury are desirable. The relativeproportions of the metal amalgamating with the mercury that have to beutilized, are dependent upon the melting points of the metals that areamalgamated with the mercury, and the temperature encountered. Thus, ifthe mercury is heated, when the tin is added thereto, as much asfifty-nave percent tin can be included in the putty-like amalgam. Thusthe paste-likeainalgam used in my method may contain between 45% and 75%mercury'by weight, depending upon the temperature at which the same isapplied to the sheet.

In making up the putty-like, or creamy, pastelike amalgam, it isnecessary that the metal that is to be dissolved in the mercury, oramalgamated therewith, is in a finely divided condition when it is to beamalgamated with the mercury. The tin, or similar metal, can be in theform of any small particles, such as shavings, turnings, cuttings, or inthe form of a powder or granules. The finely divided tin, or similarmetal, is stirred into the quantity of mercury that is to be utilized tomake the amalgam in the proportions necessary substantially within thelimits above referred to. At ordinary room temperatures, it isunnecessary to heat the mercury to cause the tin to be dissolved. unlessa relatively large quantity of tin is to be incorporated in the amalgam.After a thorough stirring of the finely divided tin in the mercury, theamalgam is formed. However, if low temperatures are encountered, atwhich the mercury will have a more sluggish character, and at which theamalgamation will not as readily occur, or in case it is desired tospeed up the amalgamation of the mercury and the tin, or similar metal,or increase the proportion of tin to be included in the putty, abovethat readily amalgamating with the mercury at room temperature, themercury may be heated for this purpose, keeping the temperature of themercury well below that at which it would vaporize.

The soft putty-like amalgam of tin and mercury produced as referredto-above, is applied to the cleaned area, or zone, of the galvanizedsheet, by brushing or rubbing the same onto, the cleaned area of thesheet with a cloth, or similar member, this rubbing or brushingoperation spreading the tin-mercury amalgam over the cleaned area of thesheet and causing a thin layer thereof to adhere to the outer surface ofthe zinc coating on the sheet, and in case there is a rupture or dam--aged area in the sheet, from which. the zinc has been entirely, orsubstantially entirely, removed, the tin-mercury amalgam will adhere tothe sheet at this point also., As soon as the tinmercury amalgamcontacts the zinc coating on the sheet, it begins to react therewith toamalgamate the zinc in the zinc coating with some of the mercury in thetin-mercury amalgam. Accordingly, in brushing the amalgam back and forthover the ruptured area, some of the zinc of the galvanizing coating willbe caused to be spread over the ruptured area, and any loose flakes orparticles of zinc will be dissolved in the tin-mercury amalgam,amalgamating with the mercury therein.

The action between the zinc and the tin-mercury amalgam will continueuntil the tin-mercury amalgam has penetrated the entire zinc coating ofthe sheet down to, at least, the ferrous zinc alloy at the surface ofthe iron or steel of the sheet. After the zinc is amalgamated with themercury, the resulting amalgam that is produced will gradually becomestiffer and harder,

as the greater the amount of other metal amal-.

gamated with the mercury, the harder or stiffer the amalgam will become.As a result, the penetration of the zinc by the mercury-tin amalgam willeventually produce a zinc-tin-mercury amalgam protective coating on thesheet over the entire surface to which the tin-mercury amalgam has beenapplied, which has lost the soft character of the tin-mercury amalgamand will become as hard as the zinc coating originally on the sheet.

Thus the amalgam, when first placed on the sheet'treated in the abovemanner, will be soft enough that it can be rubbed of! on the fingers toa certain extent. and after at least twentyfour hours the coating at thearea to which the amalgam has been applied will be hard enough thatnone'of the same will rub off and the sheet can be handled without anydamage to the amalgam coating, just as readily as was the case with thezinc coating originally on the sheet. Also, after several days the sheetwill have substantially the same appearance as it did before any amalgamwas applied thereto, and none of the coating can. be rubbed off, eventhough it may be rubbed persistently for a considerable period of time.The action of dilute sulphuric acid and other dilute acids, on the zincand tin will be retarded to such an extent that the amalgamatedgalvanized sheet produced by my method, can be successfully used wherean ordinary galvanized sheet would have such a short life that its usewould be impractical.

While my improved method is particularly adapted for use to preventcorrosion at ruptures in coatings on galvanized sheets at bends therein,or similar places, it is obvious that under certain conditions it wouldbe desirable to apply thecleaning step and the coating step, not only tothe area of a sheet on the outer side of a bend at and adjacent thebend, but also to the entire surface of the sheet, that is innermostwhen it is put in place as a wall portion of a container that issubjected to the corrosive action of sulphuric acid, or other sulphurcompounds, which are ordinarily found in oil tanks, or similarreceptacles. These sulphur compounds cause a corrosive action on thezinc coating of the sheet as ordinarily provided in oil and similartanks. However, by utilizing my protective coating, including thetin-mercury amalgam, and applying it to the inner surface of an'oiltank, or the sections of an oil tank, made up of sheets that have beenbent, out and punched, this undesirable corrosive action is avoidedentirely.

The tendency of the sulphur compounds, when acting on thezinc-tin-mercury amalgam coating. is to cause the mercury in the amalgamto form a protective film on the surface that is exposed to the actionof the dilute sulphuric acid, or hydrogen sulphide, or other sulphurcompounds,

this causing some slight loss of some of the other metals from thecoating, such as the zinc and tin, but the mercury arresting this losssubstantially immediately, due to the film forming action that it has.

There is substantially no loss of mercury in the carrying out of mymethod, because, if there is any excess of amalgam applied to the sheet,such excess can be removed with a cloth, such as the cloth by means ofwhich the putty-like amalgam has been rubbedon the sheet. and the partthus removed saved for use on another sheet or other .portion of thesheet.

While it is immaterial whether the amalgam coating is of the samecomposition throughout, it has been found that 4 if the soft putty-liketin-mercury amalgam, above referred to, is utilized, some of the mercuryin the tin-mercury amalgam will amalgamate with the zinc immediately,forming a zinc-tin-mercury amalgam, and some of the tin-mercury amalgamwill be present without any zinc in it at first, this being on the topsurface of the coating. However, if the tin-mercury amalgam is left incontact with the zinc coating for'twentyfour hours or more, and,anexcessive amount of the tin-mercury amalgam is not used, sufficient ofthe mercury will amalgamate with the zinc that all of the zinc willbecome amalgamated with mercury, and the resulting coating will be atin-zinc-mercury amalgam, from the 65.8% zinc, 13.7% tin and20.5%jmercury. with tin and 60% mercury by weight is utilized forapplication to a'galvanizedsheet that has a coating thereon-of zinc thatamounts to one ounce persquarerunning foot, or one-half ounce per squarefoot surface on each side of sheet, the amalgam resulting will containapproximately heavier coatings of zinc the percentage of zinc Theapplication of the putty-like tin-mercury I amalgam to the sheet thathas previously been galvanized results in the dissolving of the zinc onthe sheet inthe mercury of the tin-mercury amalgam, but the resultingliquefaction of the coating material on the sheet takes place throughthe thickness of the zinc coating thereon at such a slow rate that thestructure of the zinc coating on the sheet is not altered, although thecomposition changes from substantially pure'zinc to a zinc-tin mercuryamalgam as the amalgamating' process proceeds through the coating. As aresult the characteristic spangles of the galvanized sheet remain afterthe amalgamation is completed, the sheet having substantially the sameappearance two or three days after the amalgam has been applied theretoas it had before any application of amalgam was made thereto.

When a putty-like amalgam containing 40% will, of course, be'higher, andof course,.the percentage of tin will be less where an'amalgamcontaining a larger percentage of mercury is utilized. As in all casesthe amount of zinc in the amalgam will be over the coating will not losethe characteristics of a zinc coating com- .pletely, but will bemodified in its corrosion resist-j ing characteristics to a considerableextent by manner to destroy the crystalline structure of the zinccoating, while by using the putty-like amalgam in my method, theappearance of the galvanizing coating remains unchanged.

What I claim is:

The method of repairing a rupture in the zinc coating of a galvanizedmetallic sheet, comprising spreading a soft, creamy, putty-like amalgamof mercury and tin containing from 45% to mercury by weight over thesurface of said sheet at and adjacent said rupture, rubbing theresulting amalgam over said'rupture, removing all the excess amalgamfrom said sheet and permitting the resulting amalgamation, over theentire area over which the same was spread, to proceed undisturbedthroughout the thickness of said zinc coating over said area until ahard amalgam coating over said area having the spangled appearance ofthe galvanizing coatingon said sheet, is produced.

' HENRY L. KQHLER.

